What are the characteristics of DNA structure?

DNA structure contains two linked strands that twist around each other that resembles a twisted ladder shape, also known as a double helix. Each of these strands has a backbone composed of a sugar phosphate group; the backbone is on the outside of the double helix, and the sides connecting the molecules is where the sugar-phosphate groups are located. These sugar-phosphate groups are very stable and are difficult to break without specific enzymes. The backbone of DNA is negatively charged because of the bonds between the phosphorus and oxygen atom. A phosphate group has one negatively charged oxygen atom, and thus a strand of DNA is negatively charged due to the repeated phosphate groups.

Attached to each of the sugar molecules is one of the nucleotide bases: cytosine, adenine, guanine, or thymine.  Each nucleotide base is composed of a deoxyribose sugar, a nitrogenous base and a phosphate. Adenine always binds to thymine, and guanine always binds to cytosine. The bases are held to one another by hydrogen bonding, and the protein DNA ligase fuses sugar-phosphate groups of adjacent nucleotides to make up the DNA backbone. These are known as phosphodiester bonds, which are covalent in nature and are stronger than simple hydrogen bonds.